The present invention relates to an optical disk information recording medium which makes it possible to use optical disks of a CD (compact disk) type in ISO standard optical disk equipment.
Disk-shaped information recording media of 5 inch size and 3.5 inch size, for example, are classified according to physical configurations and record/reproduce modes, into CD type optical disks as shown in FIG. 5, and ISO standard optical disks as shown in FIG. 6.
The CD type optical disks of various kinds are compatible among them so that each of them can run on a single common reproducing system. Similarly, the ISO standard optical disks are compatible so that a single reproducing system suffices to replay all the ISO standard disks.
In general, an ISO standard optical disk system is provided with an optical pickup which can read not only the ISO type disk but also the CD type disk, so that the CD type disk can be replayed in the ISO equipment if the CD disk can be loaded in the ISO equipment, as disclosed in Japanese Patent Provisional Publication 3-185689. An optical disk recording medium shown in this Japanese document utilizes two detachable chucking elements attached to the center hole of an optical disk on both sides. It is, however, troublesome to attach and detach the two chucking elements.